I haven’t had the opportiunity to “deconstruct” what there is there yet, and Paul’s already had a pretty good go at it. They have withdrawn some IP as is their right during the FCC process, although at this frequency under the regs in that section of the spectrum it’s hard to believe there’s any particularly magic sauce in there. I’m surprised they’re operating so low in frequency, the wavelengths are too long to be able to do much concentrated beamforming. Even then there are ERP and power density limits.

On a side note, unlike 2.4 gigs where there is reasonably uniform global agreement, the regs around the UHF 900 megs frequency area vary very widely across and within the ITU regions globally. 915MHz isn’t even available globally, 860 megs is a common alternative, but the ERP, modulation requirements, bandwidths, channelisation, peak and average powers, plus duty cycle requirements vary greatly.

While there is no guarantee of protection within any unlicensed ISM bands, I can imagine there are enough UHF devices about such as vehicle key fobs that will no longer function with this technology in the vicinity.

Irrespective, what I certainly haven’t seen is any evidence of a practical and viable device that would come even close to expectations of the general public.

To see the multitutes of fawning proles’ comments on the various unquestioning but supposed “tech” sites is just sad. The investors, well, they’re just funding a bubble and a couple of fancy cars for the wide boys.

The parallels to uBeam modus operandi are there to be seen: with apologies to our Danish friends for paraphrasing, the Emperor is indeed wearing fuck all.

I did another couple of posts on Energous, the latest one shows that they are essentially sitting at the SAR limit, so for safety they'll not be able to increase power from where they are right now. Further, they have so little control over the beam that the highest power is rarely at the charging location.

A few more Energous posts over the weekend if anyone is interested - those with a knowledge of RF and FCC regulations, feel free to jump in or send me comments, especially if you have SAR/MPE experience.

I didn't read everything thoroughly so maybe I missed something, but my reading was that the 30mW figure in the FFC doc was a minimum before it shut off. Similarly the 100mW quoted above says "greater than 100mW", so the actual power could be a lot more ( though probably still useless)

I didn't read everything thoroughly so maybe I missed something, but my reading was that the 30mW figure in the FFC doc was a minimum before it shut off. Similarly the 100mW quoted above says "greater than 100mW", so the actual power could be a lot more ( though probably still useless)

Yes, it doesn't send power if the receiver doesn't say, via bluetooth, that there's at least 30 mW being received (not clear if RF or at battery). Since it works out to 90 cm, then it's pretty clear it's 30 mW at 90cm. Energous say "at least 100 mW received" at 50 cm, and if it was 200 mW they'd say "at least 200 mW" etc. Also, from SAR calculations you can work out what the power is (you can see it in the SAR plots) and I detail it in this post here: https://liesandstartuppr.blogspot.com/2017/12/energous-it-just-keeps-getting-worse.html

They provide most of the data that allows you to work this out in the FCC data (legally they have to), though you do have to jump through some hoops. It looks to be about 100 mW received at the battery at 50cm, under ideal circumstances, with perfect orientation, at 1% efficiency, on the edge of a safety zone.

I am slightly confused here: the maximum total radiated power allowed on 915MHz ISM in Part 15 is 36dBm (4W) EIRP.

The maximum total transmitter power allowed is 30dBm (1W).

Edit: as this is technically not a telecommunications device, it's covered by Part 18. I need to brush up on my Part 18 I guess.

I go into a lot of depth about the differences between Part 15 and Part 18 in my blog, but this is the first "wireless power" device to get approval under Part 18 which is sometimes termed "unlimited power". It's really "unlimited transmission until you hit other interference or safety limits". They claimed that because they are beaming power to a specific location, and because they have a "safety cutoff" which switches the system off if there is movement within 50cm, it's safe and meets requirements. There are 12 antenna each capable of putting out around 0.875W, so roughly 10 Watts total output. Looking at the numbers, at 50cm from this system they sit at the Specific Absorption Rate limit, which means they can never increase from there. Also if you look at the field profiles they really have very little control over where the power goes, as they have few antenna in a small line, large wavelength and are in the near-field. It's a terrible system, the safety cutoff is a joke and will fail in trivial to consider conditions, and the power delivered is very low even under ideal circumstances (1% efficiency is the ceiling for how good it gets).

I've links to the FCC regulations in the posts here. They're painful as it's all spread across multiple documents, and not easy to read - and I'm used to reading FDA regulations...

Irrespective, it should be noted that the 915MHz ISM band is an ITU Region 2 (the Americas) allocation only, and Parts 15 and 18 are only the US’s implementation. Whether similar Part 18 rules apply outside the US, such as in Canada on 915MHz for example, I don’t know.

As far as I am aware, the other two regions have have nothing close except within Region 1 (EMEA) where Europe has an 868MHz band but it’s less power, limited duty cycles and includes mandatory interference avoidance protocols at anything above a very low power level.

This is one of the reasons that 915MHz isn’t used so much, it’s just not a global standard. However it is comparatively generous on power under Part 15 in the US.

So, we can safely say that this is not going to be a global product in its current form unless you can get the regulatory powers to agree, good luck with that.

As an aside I wasn’t sure in one of your notes where you mention different element spacing requirements on different bands, and where that comes from? In general at these frequencies where ground effects are less significant, typical spacing is around lambda/2 for reflective arrays or patches. You can tweak it a little depending on whether you can compromise on side lobes and front to back etc, but not usually by much in air.

One way they may have well have reduced size is to use patches with a dielectric substrate with permittivity Er>1. This slows the wave propagation so you can make physically smaller antennas, usually at the expense of some efficiency as solid dielectrics tend to be lossy. This is common at S band and higher, but not so much below. Of course this also affects the interference pattern of the phased array, so you need to address that too.

Irrespective, it should be noted that the 915MHz ISM band is an ITU Region 2 (the Americas) allocation only, and Parts 15 and 18 are only the US’s implementation. Whether similar Part 18 rules apply outside the US, such as in Canada on 915MHz for example, I don’t know.

As far as I am aware, the other two regions have have nothing close except within Region 1 (EMEA) where Europe has an 868MHz band but it’s less power, limited duty cycles and includes mandatory interference avoidance protocols at anything above a very low power level.

This is one of the reasons that 915MHz isn’t used so much, it’s just not a global standard. However it is comparatively generous on power under Part 15 in the US.

So, we can safely say that this is not going to be a global product in its current form unless you can get the regulatory powers to agree, good luck with that.

As an aside I wasn’t sure in one of your notes where you mention different element spacing requirements on different bands, and where that comes from? In general at these frequencies where ground effects are less significant, typical spacing is around lambda/2 for reflective arrays or patches. You can tweak it a little depending on whether you can compromise on side lobes and front to back etc, but not usually by much in air.

One way they may have well have reduced size is to use patches with a dielectric substrate with permittivity Er>1. This slows the wave propagation so you can make physically smaller antennas, usually at the expense of some efficiency as solid dielectrics tend to be lossy. This is common at S band and higher, but not so much below. Of course this also affects the interference pattern of the phased array, so you need to address that too.

SAR limits are global - they are slightly higher outside of US, Canada, Korea but 2 W/kg not 1.6W/kg, so they could go up by 25% internationally but that's 25% of not-a-lot. Part 18 etc or frequency band is irrelevant outside that.

The different element spacing at different frequencies is just down to lambda/2 spacing as typically ideal, as lambda changes with frequency. Energous are at 0.2 lambda spacing right now, 33cm wavelength with 6cm pitch, which is on the verge of "just halve the number of elements and drive each twice as hard" as far as a phased array goes. They also only have 12 antenna total, so have very limited control over beamforming as can be seen in the plots where power seems to go everywhere but at the target.

I do mention patch antenna but there are two further issues there - first is that the impedance goes up so for any given voltage induced you have lower power, second is that they are highly directional so on receive it's hideous. It's bad for send too, you're already at 1% efficiency at best, but I doubt they are concerned about that.

I didn't read everything thoroughly so maybe I missed something, but my reading was that the 30mW figure in the FFC doc was a minimum before it shut off. Similarly the 100mW quoted above says "greater than 100mW", so the actual power could be a lot more ( though probably still useless)

That was my reading too.But you can calculate the max possible figure based on input power (known), the max capture area of a phone (known) and say 6dB antenna gain or something.

I didn't read everything thoroughly so maybe I missed something, but my reading was that the 30mW figure in the FFC doc was a minimum before it shut off. Similarly the 100mW quoted above says "greater than 100mW", so the actual power could be a lot more ( though probably still useless)

That was my reading too.But you can calculate the max possible figure based on input power (known), the max capture area of a phone (known) and say 6dB antenna gain or something.

The recent FCC filing for demo at CES shows it's a factor of 3, or 4.8dB gain, starting with 10 W antenna power, so 30 W ERP and 50W EIRP. Plugging those numbers into the Friis equation (very approximate as it's near field at those wavelengths) you get around 140 mW at 0.5 meters and 40 mW at 0.9m. That's RF received and does not include conversion efficiency which will be 60 to 70%, so at 70% that would be 100mW and 30 mW approximately, which tie with the numbers you see reported (especially the 30 mW at 90cm in the FCC filing).

SAR limits are global - they are slightly higher outside of US, Canada, Korea but 2 W/kg not 1.6W/kg, so they could go up by 25% internationally but that's 25% of not-a-lot. Part 18 etc or frequency band is irrelevant outside that.

My point was really around the band they're using is simply unavailable outside Region 2, so it can never be a global product. I don't know what restrictions Industry Canada put on the band, for example, I couldn't readily find reference to their equivalent of Part 18. Although Part 15 will be fairly commonly reflected around Region 2, with some local technical provisos, there may not be any equivalent provision at all for an equivalent of Part 18 on the 915 MHz band. Certainly the regulations I'm aware of, although admittedly in telecomms, tend to be pretty prescriptive and vary significantly.

I am somewhat surprised that despite the prescriptiveness of Part 15 (specific EIRPs in specific circumstances, channelisation, modulation methods, spread spectrum etc) as a means to allow and encourage interoperability on an inherently shared spectrum, is almost completely nullified by Part 18 which allows anything as long as the SAR requirements are met!

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The different element spacing at different frequencies is just down to lambda/2 spacing as typically ideal, as lambda changes with frequency. Energous are at 0.2 lambda spacing right now, 33cm wavelength with 6cm pitch, which is on the verge of "just halve the number of elements and drive each twice as hard" as far as a phased array goes. They also only have 12 antenna total, so have very limited control over beamforming as can be seen in the plots where power seems to go everywhere but at the target.

I do mention patch antenna but there are two further issues there - first is that the impedance goes up so for any given voltage induced you have lower power, second is that they are highly directional so on receive it's hideous. It's bad for send too, you're already at 1% efficiency at best, but I doubt they are concerned about that.

The only options I can think would work would be a reflective planar array or a patch array. Planar arrays would have greater physical depth, there's a need to have some distance between the passive reflector and the driven element. Increasingly a patch array seems likely to me. My reasons for thinking this are multifold.

o Firstly, they can be fabricated using common microstrip techniques cheaply using double sided PCB, with all six driven elements fabricated on a single PCB.

o Secondly, the PCB substrate will have a permittivity that will significantly shrink the patch and spacing, with typical Er's of PCB allowing about half the size of a patch in air.

o Thirdly, driving these patches can be done very close to the driven elements, with active components including both HPAs and phase shifting. Distributing the parts to each driven element, particularly the HPAs in this way, has both thermal and loss benefits.

o Finally, polarisation. Implementing circular polarisation on a PCB fabricated patch is simple to achieve, but will need some spaghetti wiring on a reflective array. Circular polarisation has the benefit of significantly reducing fade as it's not dependent on device orientation on a given plane.

Regarding the impedance of patches, in my experience (I work on antenna designs primarily for ground and space segments in aerospace, but also work in terrestrial stuff too) that's really a non-issue particularly in narrow band applications like this. This can be done either with microstrip matching transformer techniques fabricated into the substrate, or, quite likely at 915MHz, with simple lumped fixed LC parts especially as the substrate is (as is likely) simple PCB material.

Regarding directionality of the patch, an identical issue occurs with a reflective array element. Both have broadly similar directivity and gain (about 6dBi, especially if the patch is fabricated on solid dielectric substrate).

So far I've only discussed the sending antenna. I'm not sure what physical form factor the receive side takes, I guess it's probably a sleeve. A problem here is to get something that's of a reasonable size and efficient at the frequency of interest, and, as you say, isn't too directive. In addition, achieving reasonable polarisation matching is going to help: in a linearly polarised system if you're rotated 90 degrees off in a facing plane, almost no power will be received. If the transmitter is circularly polarised instead then these nulls can be removed. If the receiver is also circularly polarised with the same sense, then minimal losses will occur.

There is however an engineering problem in that getting an efficient circularly polarised antennas in a reasonably sized phone sleeve envelope is going to be compromised. It may be better to accept that the sleeve receiver side remain linearly polarised and accept the 3dB hit incurred converting from circular to linear, as you'll get a more consistent experience that with both sides being linearly polarised. It will also mean that the receiver can harvest energy in many more three dimensional orientations.

Maintaining decent circularity with phased arrays significantly off the default centre boresight adds complexity but can be engineered if only one device is being targeted. Maintaining a reasonable axial ratio (i.e. good circularity) would be necessary to avoid nulls similar to those found using a linear-only solution.

One further concern I have on the solution as a whole is over multipath. Almost certainly there are going to be dead spots with this solution in any practical installation, and even a phased array isn't going to fix this, although it could, if you're really smart, achieve some mitigation by adjusting polarity on the fly.

Frankly all of this, while academically interesting, if I may mix metaphors, is putting lipstick on a pig that's never going to fly.

I didn't read everything thoroughly so maybe I missed something, but my reading was that the 30mW figure in the FFC doc was a minimum before it shut off. Similarly the 100mW quoted above says "greater than 100mW", so the actual power could be a lot more ( though probably still useless)

That was my reading too.But you can calculate the max possible figure based on input power (known), the max capture area of a phone (known) and say 6dB antenna gain or something.

The recent FCC filing for demo at CES shows it's a factor of 3, or 4.8dB gain, starting with 10 W antenna power, so 30 W ERP and 50W EIRP. Plugging those numbers into the Friis equation (very approximate as it's near field at those wavelengths) you get around 140 mW at 0.5 meters and 40 mW at 0.9m. That's RF received and does not include conversion efficiency which will be 60 to 70%, so at 70% that would be 100mW and 30 mW approximately, which tie with the numbers you see reported (especially the 30 mW at 90cm in the FCC filing).

I may well have mis-read/misunderstood, but that 30W applies to the ERP which is a transmit segment system parameter, independent of the receive side.

There are also some inconsistencies in the application.

You can achieve a ballpark estimate of the tx antenna gain from its half power beamwidth, which is 30 degrees. This approximates in the real world to about 16dBi. This approximation assumes a single major lobe of course. To achieve 30W ERP (50W EIRP) with 16dBi gain, you need 1.25W transmit power. 16dBi is also just about reasonable for a 12 patch array

Curiouser and curiouser, although admittedly I am basing these rough figures on a square* rather than rectangular array, and using far field calculations and derivations, but then those are the figures generally used for E(I)RP calculation.

* Another point I neglected to mention is that they are using a linear rather than planar array. This will of course only allow beam forming along the horizontal axis.

Thanks for the posts on RF there, very good information. It's great to be on forums like this with people who have deep expertise to learn from. A few points to answer some of your questions:

1) The answer to a lot of questions as to "Why is their system making this dumb choice?" is "They designed for 5.8GHz but were repeatedly denied approval and had to change a lot of stuff rapidly. Sole priority was to get Part 18 approval." Always remember that when evaluating anything they do!2) Very good point that while Part 15 is more recognized internationally, and that Part 18 is not.3) The system just approved for the demo may be different than the FCC system, so my statement on 10W transmitted may be incorrect, though I can't see how the power can be much higher due to safety regulations. They may have a system that concentrates the same power more. We'll see at CES.4) The reason they went with 913 MHz is FCC part 18 rules - there are very specific bands where the unlimited power applies. ~0.913, 2.4, 5,8, 24GHz. They were denied at 5.8, used 2.4 for their communications (and would have likely been denied there too for the same reasons as 5.8 ), so it was 913 MHz or 24 GHz. No other way to get FCC Part 18 approval.5) If you look at the FCC approved transmitter, you can see the arms where the antenna are positioned changes in thickness, it's never more than about 5cm, I do not believe they'd have space for a reflective planar antenna with a 33cm wavelength.6) The FCC approval says that the receive power is extremely sensitive to angle, it's unlikely to be circular as opposed to linear.7) Good point on matching the antenna impedance - I tend to work on arrays with hundreds or thousands of elements so matching each is not practical. Also I'm more broadband than narrowband when I do imaging. It is more viable with the smaller number of elements in this application.8 ) The antenna do not have to be the same for send as receive - e.g. patch antenna for transmit, half-wave dipole for receive.9) Yes the phased array arrangement is awful, limited control especially vertically, and there are huge hotspots/deadzones. Will be interesting to see if there is a difference between the CES and FCC arrays.

Finally, "lipstick on a pig" is a kindness for this system, it's far uglier than a pig.

Summary is that the demo is everything you would expect with small distances and useless power levels. Energous show off Mid-Range systems not approved by the FCC hoping that they'll be mistaken for the FCC approved one, and even extend this tactic to their already approved Near Field contact system which is now incompatible (5.8 GHz vs 0.9 GHz), and call all of them "WattUp", successfully confusing journalists that it's all one integrated technology. A triumph of marketing.

Going by PR's calcs, I think it's more like 15 - 20 kWhrs. About 4 times more expensive than buying 2 new AAs.

For the keyboard yes, should be <1% efficient from what I've seen, maybe higher as it's close, maybe lower as the antenna are horizontal. An AAA battery is around 1 Wh and an AA 2 Wh, IIRC, so 50 to 100 hours per battery at that 2 mW, 15 to 30 at the 67 mW, and power consumption in the low 100's of Wh, if we're generous. 1 kWh isn't impossible. My wireless keyboard has been going over 2 years without issue right now, not seeing the desperate need for this...

I actually haven't bothered to do the calculations of efficiency for the contact charging device, which the underwear uses, as it is such a pointless product. Qi has won here, it's all variations on that from here on out. All the Near Field charger exists for is to muddy the waters for the Mid-Range performance by calling them all "WattUp" despite the differences.

I watched that Tom's Guide video a couple of days ago, and I had very similar views, I even attempted to write a comment but the entry to commenting was too cumbersome and irritating to bother.

The Tom franchise is definitely not what it once was. For example very frustratingly, they arbitrarily close completely unsolved problems with the words "SOLVED" in the title, I am sure it is clickbait and gets it into Google rankings as a result. No longer is it a trustworthy platform I'm afraid.

Regarding the video itself, as soon as I saw the devices within a few inches, and within the FCC approved 50cm keep-out area, it confirmed that this was a scam. Yes, they do have FCC approval, just not for what they demonstrated! Aaarghhh!

The conflation and confusion of cross-branding was also irritating, but that sort of marketing wank regrettably is not really unique to Energous.